Despite numerous studies on hydrochar use, its application in water treatment for pathogen removal remains unexplored. In this study, we evaluated the efficiency of hydrochar produced from crop residue of maize for water treatment by determining Escherchia coli breakthrough from sand columns supplemented with hydrochar. To enhance the adsorptive capacity, raw hydrochar was activated by 1 mol L^-1 KOH at room temperature. The experiments conducted in a 10-cm sand bed with 1.5% (w/w) activated and raw hydrochar supplements, not activated by KOH, showed 93 and 72% of E. coli removal efficiencies, respectively. Activation of KOH not only enhanced the E. coli removal but also increased the strength of the attachment: 96% of the E. coli retained in the column with activated hydrochar supplements was shown to be irreversibly attached, compared with only 65% for the raw hydrochar. Scanning electron microscopy/energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and zeta-potential analyses suggested that these improvements were mainly due to the development of a wellformed porous surface structure and less negative surface charges on the activated hydrochar.